Scanning device



G. L. DKMMKZK SCANNING DEVI-SE Nov. 26, 1940.

Filed Sept. 21, 1957 INVENTOR. GZE/l/V LESL/E D/MM/CK X/WW ATTORNEY.

Patented Nov. 26, 1940 UNITED STATES SCANNING DEVICE Glenn Leslie Dimmick, Radio Corporation of Delaware Erlton, N. J., assignor to America, a corporation of Application September 21, 1937, Serial No. 164,847

3 Claims.

This invention relates to a method of and means for producing a scanning operation.

More particularly, the device is concerned with means for scanning an area by a beam of light in order that the light values of the area so scanned may be transformed into electrical variations. The invention is further concerned with the scanning of a tape for facsimile transmission wherein the tape is gradually and continuously moved through the scanning device while at the same time a beam of light is caused to traverse the width of the tape in order that indicia or characters on the tape may be transformed into electrical variations representative thereof.

Heretofore rather cumbersome and ineiiicient means such as rotating or vibrating mirrors, for example, have been provided for so deflecting a beam of light that it may be caused to traverse the entire or substantially the entire width of a tape on which various markings have been previously placed and it is therefore one purpose of the present invention to provide a means for producing a scanning operation which is simple and efficient in operation.

A further purpose of the present invention is to provide a facsimile scanning device which is compact and rugged and which includes a minimum of moving parts. A further purpose of the present invention is to provide means whereby a beam of light may 'be caused to scan an area in one direction only, by the use of a multi-sided prism through which the light is permitted to pass.

A still. further purpose of the present invention is to provide a multi-sided prism though which a narrow beam of light is projected, the beam of light being accordingly subjected to a certain degree of refraction depending upon the angle at which the beam of light strikes the prism.

A still further purpose of the present invention is. .to provide an apparatus wherein a beam of light may be caused to be deflected in more than one direction, whereby a stationary area may be scanned by asingle continuously moving beam of light.

'Still further advantages and purposes of the present invention will become apparent to those skilled in the art from the following specification, particularly when considered in connection with the drawing, wherein:

Figure 1 represents, schematically, a device for scanning a tape or other surface, the device being constructed in accordance with the present invention;

Figures 2, 3 and 4 show various positions of the (Cl. IVS-4.6)

refracting prism and the effect that the positions of the prism have upon the beam of light; and,

Figure 5 shows a modification of the present invention as applied to two-way light beam deflection.

Referring to the drawing, in Figure 1 is shown a source of light It} and condensing lens system II for concentrating the rays of light from the source into a beam. A mask 12, having an aperture I3 is placed in front of the condensing lens in order that a small beam of light may be produced and in order that the shape of the beam may be controlled. This beam of light is projected against a multi-sided prism I4 which is appropriately mounted on a shaft l5 for rotation therewith. On the opposite side of the prism is positioned an objective lens system 22, whereby the beam of light after having passed through the prism may be brought to focus upon the surface of a character bearing tape 24 such as at point 25. The light is then reflected from the tape in accordance with the light values of the tape as determined by the characters provided thereon, and is collected by the lens 26 and projected upon the photo-sensitive or light responsive cell 2?. V

The beam of light is preferably rectangular in cross section and sufficiently reduced in area so that the characters or indicia on the tape may be legible when reproduced at the receiver. Any appropriate means may be provided for rotating the prism about its axis, and as the prism is rotated, the light in passing through the prism is caused to be refracted by varying degrees depending upon the angle at which the light strikes the faces of the prism. The speed of rotation of the prism and the advancement of the tape are such that the tape moves an amount equal to the width of the beam of light for each traversal of the beam of light and each complete revolution of the prism causes as many beam traversals as there are faces or sides on the prism. The mechanism for moving the tape and for rotating the prism are preferably mechanically connected together in order that the relative movements of the two elements may be maintained constant. However, this is not necessary since independent means for driving the prism and the tape may of course be employed.

By referring to Figures 2, 3 and 4 the manner in which the beam of light is refracted may be clearly understood. Assume, for instance, that in Figure 2 the beam of light is projected toward the axis of the prism, but at substantially right angles thereto, and that the prism is so positioned angularly that the beam of light strikes one face of the prism at an angle of 90 degrees. No refraction of the light upon entering the prism will therefore result and the light beam will continue directly through the center of the prism and will leave the prism normal to the diametrically opposite surface from which it entered. If the prism is rotated counter-clockwise by a certain amount, as shown in Figure 3, the beam of light will not strike the surface of the prism at an angle of 90 degrees, and as a consequence the beam of light will be refracted upon entering the surface and will not pass through the geometrical axis of the prism. When the beam of light leaves the diametrically opposite side of the prism, a refraction in the opposite direction takes place so that the leaving beam of light is parallel to the entering beam of light, but is laterally displaced therefrom by an amount depending upon the angle at which the light strikes the face of the prism and the size of the prism. If the prism is rotated a further amount in the counter-clockwise direction, as shown in Figure 4, such that the beam of light will strike the next face of the prism, the beam will then be refracted in the opposite direction and again will not pass through the geometrical axis of the prism and, upon emerging from the prism, will travel in a path parallel to the path of the entering beam but will be displaced laterally in a direction opposite to that in which it was displaced in Figure 3. It may therefore be seen that as the prism is rotated, the beam of light, after having passed through the prism, will be deflected or displaced in a plane perpendicular to the axis of the prism by an amount depending upon the size of the prism and the number of faces. In the particular embodiment shown a six-sided prism is used, although it is obvious that a different number of sides or faces could as well be used. It is preferred however, that an even number of faces be used in order that the entering and leaving beams will be parallel and in order that the refraction of the beam upon entering and leaving the prism will be the same. Otherwise, if an odd number of faces are used, the refraction of the beam upon entering and leaving the prism will not be the same and chromatic dispersion will result.

In Figure 5 is shown a means whereby the beam of light may be deflected in more than one direction in order that a stationary area may be scanned. In this instance the prisms 28 and 30 are mounted at an angle to each other and are each provided with means whereby they may be rotated. The prism 28, when rotated in the direction shown by the arrow, will cause a deflection of the beam in a vertical direction over the area to be scanned as indicated by the arrow y. The prism 30 when rotated in the direction of the arrow will cause a deflection of the beam in a horizontal direction as indicated by the arrow 1. The speed of rotation of one of the prisms (as, for instance, the prism 30) is, of course, in excess of the speed of rotation of the other prism and preferably the two prisms are mechanically connected together and driven by a common prime mover in order that their relative movements may be fixed. The speed of rotation of the prism 30 is as many times greater than the speed of rotation of prism 28, as there are horizontal lines to be scanned in the particular area 32, assuming that each prism has the same number of faces.

Although Figure 5 is shown rather schematically, the source of light, lens systems, etc., not being shown, it is to be understood that in the actual use of the embodiment shown in the figure appropriate lens systems and other necessary elements will be used.

Such a system as is shown in Figure 5 may be, for instance, advantageously used in connection with the scanning of picture areas such as for television purposes or where the area to be scanned cannot be conveniently moved to provide one scanning movement. Where, however, one of the scanning movements may be imparted by movement of the surface per se, such a system as is shown in Figure 1 may be used.

From the above it may therefore be seen that a very simple and compact means for causing the deflection of a beam of light for the purpose of scanning an area has been provided, with the particular advantage that there is no time lost in returning the beam to a starting point. Furthermore, by using a light conducting element such as the prism for causing deflection of the beam, reflecting surfaces are avoided, with the result that the prism is more easily made and more permanent in nature inasmuch as no silvered surfaces are used which may, in time, become injured or tarnished and require re-sllvermg.

It is to be understood that various optical systems may be used in the present invention, since so far as the use of the system is concerned, it is immaterial whether the specific lenses shown are used or not. Obviously other combinations of lenses, either spherical or cylindrical, may of course be used. Also, appropriate light reflectors for better concentrating the light from the source may be used.

Furthermore, it is to be understood that, although a square aperture I3 is shown, other apertures of other shapes may be used, and, in fact, it is conceivable that by the use of appropriate lens systems no apertures need be used at all. Various shapes of beams may also be pro duced by the use of cylindrical lenses.

It is to be further understood that, although the device as shown is used in connection with a facsimile tape of relatively narrow dimensions, other tapes may in fact be used, and furthermore, it is not necessary that the light be collected by reflection from the surface of the tape since, obviously, a tape having certain light transmitting values could as well be used, and in which instance the light collecting means or light responsive device would be placed on the opposite side of the character or indicia bearing surface.

It is also to be understood that the present invention is not necessarily confined in its use to facsimile or similar transmitting devices, since it is conceivable that the invention could be used in a receiving device in which case appropriate light modulating means would be interposed somewhere in the optical system. When a light modulating means is used, a light responsive recording paper could then be employed in the recording device and a record of a received facsimile could be reproduced on the sensitized or light responsive paper.

Various other modifications and alterations may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be'considered within the purview of the present invention except as limited by the hereinafter appended claims.

I claim as my invention:

1. In a scanning apparatus, a source of light, a multisided light transparent prism, means for producing a narrow light beam from said source and directing the same against said prism in a direction substantially normal to the axis thereof for transmission therethrough, means whereby said prism may be rotated about its axis, a second multi-sided light-transparent prism, means whereby said second prism may be positioned with its axis at an angle to the axis of the first prism, means for directing the light transmitted by the first prism against the said second prism in a direction substantially normal to the axis thereof for transmission therethrough, and means adapted for rotating said second prism at a speed different from the speed of rotation of the first prism whereby the beam of light after passing through both prisms will be deflected in different directions and at different rates by reason of light refraction caused by the prisms.

2. In a scanning apparatus, a first and second light transparent multi-sided prism, means for positioning said prisms with their axes substantially normal to each other, said prisms being adapted for rotation about their axes at different rates of speed, and means for producing and directing a narrow beam of light through both prisms in a direction substantially normal to the axis of each whereby the beam of light will be deflected in substantially bilateral directions by refraction at each prism.

3. The method or deflecting a beam of light in two directions and along bilateral paths which comprises producing a narrow beam of light, providing a pair of light transparent multi-sided prisms, positioning the prisms with their axes at an angle to each other in spaced parallel planes, projecting the beam of light through the prisms and rotating the prisms about their axes.

GLENN LESLIE DIMMICK. 

